African swine fever has spread rapidly to more than half of China's provinces despite measures to contain it, the government said, warning that a situation previously described as under control had become "very serious".

The disease has already caused a spike in pork prices in China since first emerging in August, and fuelled growing fears of a major impact on the world's largest pig producer.

"The African swine fever prevention and control situation is very serious," said a joint statement by the ministries of agriculture, transport, and public security that was posted late on Wednesday.

"The epidemic has appeared in 17 provinces, spreading to large pig-farming provinces in southern China."

In early September government-controlled media said African swine fever had been discovered in just five provinces, with the agriculture ministry saying at the time that the virus was "generally under control".

The three ministries called for strengthened supervision of the transport of live pigs to prevent the disease spreading further.

China reported its first case in August in northeastern Liaoning province.

Since then, the disease has steadily moved south into major pork-producing provinces despite efforts to contain it, including by culling tens of thousands of pigs.

The ministries blamed the spread on the flouting of restrictions imposed on moving pigs out of affected areas.

The United Nations Food and Agriculture Organization (FAO) warned in August that the disease could spread to other parts of Asia.

African swine fever is not harmful to humans but causes deadly haemorrhagic fever in domesticated pigs and wild boar.

With no antidote or vaccine, the only known control method is to cull animals.

Around half of the world's pigs are raised in China, and Chinese are the planet's biggest per capita consumers of pork, according to the FAO.